The present invention relates in general to sewing machines having vertical axis rotary loop taker assemblies, and, in particular, to a zig-zag sewing machine having a vertical axis rotary loop taker allowing free passage of a thread loop about a loop taker supported, non-rotatable bobbin carrier, and having an arcuately movable, pendulumlike needle bar guide for effecting zig-zag stitching movements of the associated reciprocating needle bar.
U.S. Pat. No. 2,862,468 to Johnson discloses a zig-zag sewing machine of the general type to which the present invention is directed. Such a sewing machine includes a continually rotating, cup-shaped loop taker coaxially supporting a non-rotating thread case or bobbin carrier, the axis of rotation of the loop taker being parallel to a vertically extending, reciprocating needle bar cooperating with the loop taker.
With particular reference to the drawings of the noted Johnson patent, a loop taker mechanism (see drawing FIGS. 33-45) includes a revolving beak portion 219 that draws a thread loop about an associated thread case 283 wherein the thread loop is forcibly pulled between the non-rotatable thread case 283 and a thread case stop in the illustrated form of the distal end of a restraining arm 322. Such movement of the thread loop about the thread case is discussed by Johnson in the section of his patent specification titled "Stitch Formation."
While frictionally impeded movement of thread loops about a non-rotational thread case or bobbin carrier, between a stop and the bobbin carrier, in the manner taught by Johnson may provide suitable loop stitching, it has been recognized by those skilled in the art that unimpeded free movement of the thread loop about the bobbin carrier is more desirable since frictional wear-and-tear on the thread loop would be lessened.
U.S. Pat. No. 4,108,095 to Kohara provides a loop taker assembly having an opposed pair of movable stops which alternately impede the rotation of an associated bobbin carrier mounted coaxially upon and supported by a continually rotating loop taker. While the vertical axis rotary loop taker assembly of Kohara does preclude the necessity of forcing the thread loop between the bobbin carrier and one or more stops continuously engaging the bobbin carrier, the resultant mechanism is undesirably complex and costly to manufacture.
With further reference to U.S. Pat. No. 2,862,468 to Johnson, in drawing FIG. 19 and in lines 49-72 of column 13 of his specification, Johnson teaches the desirablility of having his stitch needle arcuately track the adjacent arcuate sector of the revolving loop taker hook path during zig-zag transverse movement of the stitch needle. The needle bar guide mechanism provided by Johnson to effect such arcuate stitch needle movement includes a pair of ball-and-socket universal joints 124, 188. Such joints are relatively expensive to manufacture and may easily become fouled with dirt over a period of time, since their bearing surfaces open outwardly and upwardly wherein settling airborne dust can readily enter.